1. Field of the Invention
The present invention relates generally to printing press circulation systems, and, more particularly, to a water pan having a dedicated power return drain and optional cooling capability located on and as part of the pan.
2. Description of Related Art
In a conventional printing press liquid circulating system, a cylindrical pan roller is partially immersed in a refrigerated or non-refrigerated liquid which is contained in a cooling pan. The pan roller is rotated to pick up the appropriate amount of cooled liquid from the pan and distribute a uniform film of liquid to the dampening system of the press.
FIG. 1 illustrates a conventional liquid circulating system. As illustrated in FIG. 1, a conventional liquid circulating system includes a circulator 110 housing a tank or reservoir (not shown) for storing the liquid and a compression refrigeration circuit (not shown) typically utilizing R12, R22 or R134A refrigerant (adopted for environmental reasons), and a pump 112.
The compression refrigeration circuit cools the liquid that is sent to either a single pan 120 or multiple pans on the printing press. The liquid fills the pan(s) 120 to a level determined by either a removeable standpipe or dam 124.
A supply conduit 114 extends between the circulator 110 and the pan 120 and provides for a relatively constant flow of liquid into pan 120. Liquid is forced through supply conduit 114 by the circulator pump 112 which is driven by an electrical motor or equivalent (not shown).
The standpipe 124 of the cooling pan drains the liquid to a liquid return conduit 116. Return conduit 116 directs the liquid back to the tank or reservoir in the circulator 110. The liquid continuously flows through the pans (while removing heat from the press) and enters the return conduit 116 by flowing over and into the standpipe drain 124. In some cases, the return flow is simply drained by gravity back to the circulator tank or reservoir. However, most pan drain hole sizes and the return line routing provisions (i.e. space, bends, and conduit paths) do not permit for simple gravity return.
The pump 112 pumps liquid through the supply conduit 114 to supply the pan with a cooling liquid and to circulate the liquid through the pan to the return conduit 116. The pump supplies liquid through the supply conduit 114 and a branch supplies the power drain to create a suction pressure (i.e. a pressure below atmospheric pressure) that is induced in the portion of the return conduit 116 between the pan 120 and the circulator 110.
Traditionally, the liquid has been cooled at the circulator 110 by the compression refrigeration circuit and then pumped to the pans 120. However, by the time the liquid reaches the pan 120, losses in cooling capacity have occurred during the transport phase through the supply lines 114. This reduction in cooling capacity reduces the ability of the liquid to remove the heat generated by the press operation.
Conventional circulators 110 have also been provided with a return line power drain 118 at the circulator 110 to create a vacuum in the return line 116 to assist return flow. For proper operation, the power drain 118 must provide a vacuum that allows for only liquid return from the standpipe 124 entry position. Too much vacuum, however, will cause foaming in the tank or reservoir as air will be drawn in, and too little vacuum will cause the pan to overflow.
With the power drain located at the circulator, the system uses cooled flow to operate the power drain. Approximately 40% to 80% of the pump output is used as motive flow for the power drain. However, as mentioned above, losses in cooling capacity occur during the transport phase through the supply lines.
A large number of press manufacturers produce a variety of presses, each having different size pan return holes, conduit lengths and shapes, space, required bends, and varying conduit return paths, creating a matrix of varying return flow conditions which cannot be handled properly with the present circulator power drains. Each pan system can have different return line lengths, bends and return line paths. Additionally, in a multiple pan system with a single power drain, ink debris in one return path will cause an imbalance and cause the return on one to flood while the rest foam.
Normally, one or more power drain sizes are used to cover this varying range by circulator manufacturers. However, these systems are hard to balance by flow control means to the power drain and are very troublesome when two or more pans are connected to only one power drain. Various attempts to control the power drain function, such as that disclosed in U.S. Pat. No. 4,300,450 to Gasparrini, have been made, but the basic problems still exist.
Another problem with power drains located at the circulator is that one return line is required for each pan to return the liquid back to the circulator tank or reservoir. These current circulating systems place limitations on the installation of conduits, resulting in unprofessional arrangements.
Thus, there exists a need for an improved printing press liquid circulating system that provides improved drain flow creating a balanced system, improved cooling capacity, ease of installation, and a more effective pan design.